Accurate mapping of normal and abnormal patterns of brain development in fetuses and premature neonates is a key factor in early detection of developmental disorders as well as understanding how external factors can influence early brain growth. In our previous funding period we developed and applied novel fetal MRI motion correction and reconstruction techniques to produce the first 3D and 4D maps of normal human brain growth in-utero and to identify early cortical folding abnormalities in ventriculomegaly (VM), the most commonly identified fetal brain abnormality. These findings pose the question of whether measureable perturbations in tissue microstructure may be present along with these larger scale anatomical differences. Such changes could provide a clearer indicator of cortical damage than simply folding alone. In this renewal we therefore propose to develop new techniques that allow the general use diffusion MRI methods in un-sedated fetal studies. These methods, previously used in adults and children, can provide a unique new window into microstructural properties of fetal brain tissue. However, the technique has an important limitation for practical whole brain fetal imaging: it makes use of repeated acquisitions where subtle changes in MR signal provide the measure of interest. Fetal head motion within the scanner can perturb measurement location, orientation and signal level due to the changing relationship between the anatomy and scanner. Our first aim is to develop a novel unified framework that can make use of image acquisition physics for correction of both signal level and measurement geometry in diffusion weighted imaging. We will then develop complementary analysis tools that can account for the varying spatial and temporal sample density in the functional and diffusion data arising from fetal head motion. We will use these techniques to image a cross-section of normal fetuses and construct a normative spatio-temporal atlas of combined structural and micro-structural measurements in the fetal brain covering the critical age of first clinical MRI scan and the following period of cortical folding. Finally, we will use te same techniques to image and analyze data from a clinical group of fetuses with ventriculomegaly with the aim of detecting early micro-structural differences that are related to our previous cortical findings in fetuses exhibiting VM. The project as a whole has many wider applications beyond this common condition and would be a major step in understanding how functional specialization in the cortex relates to brain anatomy in both fetuses and premature neonates.